1. Field of the Invention
The present invention relates to an apparatus for measuring a superior-and-inferior-limb blood-pressure index of a living subject (e.g., a ratio of an inferior-limb blood pressure to a superior-limb blood pressure, or a ratio of a superior-limb blood pressure to an inferior-limb blood pressure).
2. Related Art Statement
For a person who suffers arterial obstruction or arteriostenosis, his or her inferior-limb blood pressure ("BP") value should be lower than his or her corresponding superior-limb BP value (f or example, a systolic superior-limb BP value corresponds to a systolic inferior-limb BP value). Meanwhile, if an inferior-limb BP value of a person is higher than his or her corresponding superior-limb BP value by a certain value, he or she may suffer aortic incompetence or aortitis syndrome limited to aortic arch. It has been practiced to utilize these facts for diagnosing arterial disease based on a ratio of an inferior-limb BP value to a superior-limb BP value, or a ratio of a superior-limb BP value to an inferior-limb BP value, i.e., a superior-and-inferior-limb blood-pressure index.
Generally, the above superior-and-inferior-limb blood-pressure index (hereinafter, abbreviated to the "SIL BP index") is obtained or calculated as the ratio of a systolic BP value of an ankle as the inferior-limb BP value to a systolic BP of an upper arm as the superior-limb BP value, that is, ankle brachial index (abbreviated to "ABI") or ankle/arm BP index (abbreviated to "AAI" or "API"). If a measured ankle/arm BP index of a living person is smaller than a threshold, e.g., about 0.9, abnormality may be diagnosed on the person. Thus, even a small change of the inferior-limb or superior-limb BP value greatly affects the diagnosis.
The BP of a living person can change even in a short time. For example, the BP of a living person at rest can physiologically change by more than 20 mmHg in ten seconds. Therefore, if there is a time difference between a first time when a systolic BP is measured from an inferior limb and a second time when a systolic BP is measured from a superior limb, the BP of the person may change during the time difference. However, the conventional SIL BP index measuring device cannot enable an observer to judge, when there is a difference between an inferior-limb BP value and a superior-limb BP value, whether that difference is caused by the timewise BP change of the person or by the fact that the two BP values are measured from the different body portions of the person. Thus, the accuracy of the superior-and-inferior-limb blood-pressure index determined based on the two BP values is not sufficiently high.